Turbine blade with tip brush seal

ABSTRACT

A turbine rotor blade with a brush seal formed between the blade tip and an outer shroud to form a seal for a blade outer air seal. The brush seal includes fibers made from a high temperature resistant material that has long wear life such as fibers of alumina-boria-silicate in order to withstand the temperature environment of a turbine rotor blade and to provide long life due to rubbing of the brush fibers on the relatively rotating brush seal surface.

FEDERAL RESEARCH STATEMENT

None.

CROSS-REFERENCE TO RELATED APPLICATIONS

None.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a turbine rotor blade, and more specifically to a tip seal for a turbine rotor blade.

2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98

A gas turbine engine, such as an aero engine used to power an aircraft or an industrial gas turbine (IGT) engine used to produce electrical power, includes a turbine section with one or more rows or stages of turbine rotor blades that are exposed to a hot gas flow passing through the turbine. The rotor blades rotate within an outer shroud that forms a blade outer air seal (BOAS) to limit leakage through a gap formed between the blade tip and an inner surface of the outer shroud surface. This blade tip gap is very difficult to seal due to high temperature variations between the various parts of the turbine that form the gap. At low temperatures, the gap may be large because the blade and rotor disk have not thermally expanded in a radial direction to close the gap. At high temperatures, the blade tip may even rub against the inner shroud surface if the engine casing and the shroud expands less than the rotor disk and blades.

Brush seals have been proposed in the past for use in various parts of the gas turbine engine, but have been limited to the locations because the fibers used to form the brush seal have maximum temperature exposure limits below that of the hot gas flow. Brush seals make for very good seals, but because they are formed of brushes they tend to wear very fast. Also, brush seals do not work very well at high rotational speeds because of the high levels of rubbing that produce high frictional forces.

BRIEF SUMMARY OF THE INVENTION

The present invention is a brush seal that provides a seal between the blade tip of a turbine rotor blade in a gas turbine engine and the shroud of the engine. The brush seal can be fixed to the blade tip so that the brush seal rotates along with the rotor blade, or the brush seal can be formed as an annular brush seal fixed to the shroud in a non-rotating manner with the blade tip rotating around the annular brush seal to form the seal. In order for the brush seal to work well for a turbine blade tip seal, the brushes of the present invention are made from alumina-boria-silicate fibers (commonly known as Nextel fibers) because of the high strength and high temperature resistance. The Nextel 720 fibers have a melt temperature of 3272 degrees F. and a breaking strength of 264 ksi at 2550 degrees F., making these fibers workable for a brush seal in this particular environment.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 shows a brush seal of the present invention secured on the blade tip of the turbine rotor blade.

FIG. 2 shows a brush seal of the present invention secured on the stationary shroud and arranged as an annular brush seal.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is a turbine rotor blade for use in a gas turbine engine, where the rotor blade includes a brush seal made of Nextel fibers that forms a seal between the blade tip and the inner shroud surface of the engine. FIG. 1 shows an embodiment in which the brush seal 11 is fixed to the blade 22 tip and rotates along with the rotor blade 22 to form a seal with an inner surface of the shroud. The brush seal 11 is made of fibers of alumina-boria-silicate which is known as Nextel fibers and has very high strength and very high temperature limits. In the FIG. 1 embodiment, two brush seals 11 extend along the blade tip, one on the pressure side (P/S) and one on the suction side (S/S) of the tip to form a squealer-like arrangement. In other embodiments, the brush seal assembly can be formed from a single brush seal extending along the pressure side, the suction side or along the central portion of the tip along the chordwise direction. The brush seal 11 forms a loop around a piece 12 of the blade tip that functions to restrain the fibers in place and maintain the fibers at the proper radial distance from the tip to close the tip gap while preventing excess fibers from rubbing. The brush seals 11 in the figure

FIG. 2 shows another embodiment of the brush seal used for a turbine rotor blade. In this embodiment, the brush seal 21 is formed as an annular arrangement on the inner shroud surface 24 to form a stationary brush seal with a tip 23 of a rotor bladed 22 rotating around the annular brush seal 24 arrangement. The annular brush seal 21 is stationary and the rotor blades 22 in the stage rotate around the fibers that extend inward to form the seal. In the FIG. 2 embodiment, the fibers can be straight fibers fixed to a brush seal support since the fibers are not exposed to high centrifugal forces as in the FIG. 1 embodiment.

Other high strength and high temperature resistant fibers can be used for the brush seal on the rotor blade tips instead of the Nextel fibers as long as the other fibers have similar properties that would allow for the fibers to withstand the high temperature gas flow and the rubbing of the fibers with the shroud or the blade tips. 

1. A turbine rotor blade comprising: an airfoil extending from a root and platform; a blade tip formed on the outer end of the airfoil; a brush seal extending from the blade tip; and, the brush seal is made of fibers of alumina-boria-silicate.
 2. The turbine rotor blade of claim 1, and further comprising: the fibers are wrapped around a piece of the blade tip to form a U-shaped arrangement of fibers.
 3. The turbine rotor blade of claim 1, and further comprising: the brush seal includes a pressure side brush seal and a suction side brush seal.
 4. The turbine rotor blade of claim 3, and further comprising: the pressure side brush seal and the suction side brush seal both wrap around a piece of the blade tip to form a U-shaped arrangement of fibers.
 5. A blade outer air seal for a turbine rotor blade comprising: an outer shroud with an inner surface that forms a seal with a blade tip; a turbine rotor blade having a blade tip; a brush seal extending from one of the outer shroud or the blade tip to form a seal between the blade tip and the outer shroud; and, the brush seal is made of fibers of alumina-boria-silicate.
 6. The blade outer air seal of claim 5, and further comprising: the brush seal is fixed to the blade tip and rotates along with the turbine rotor blade.
 7. The blade outer air seal of claim 5, and further comprising: the brush seal is fixed to the outer shroud and is fixed to the outer shroud.
 8. The blade outer air seal of claim 6, and further comprising: the brush seal fibers are wrapped around a piece of the blade tip to form a U-shaped arrangement of fibers.
 9. The blade outer air seal of claim 8, and further comprising: the brush seal includes a pressure side brush seal and a suction side brush seal. 